1. Field of the Invention
The present invention relates to a security system, and more particularly to a security system which can arm and/or disarm by use of a portable transmitter unit.
2. Description of the Related Art
An anti-theft system (which is also called "a security system") for preventing a vehicle from being stolen sounds a siren or flashes the vehicle headlights when a thief opens the door, gives a considerable shock to the vehicle or opens the trunk, and also cuts off the starter of the vehicle engine (de-energizes the engine) or cuts off the supply of fuel to the vehicle, thereby preventing the vehicle from being stolen.
An example of such a security system includes one in which initiation (hereinafter called "arming") or termination (hereinafter called "disarming") of the security operation is performed by a portable transmitter remote control unit (hereinafter "Remocon" unit). The arming and disarming of the security operation are effected by pressing either an arming key or a disarming key, both provided on the Remocon unit.
In such a security system using the Remocon unit, there is a situation where the system is armed by accidental operation of the Remocon unit by the driver or passenger while the vehicle is being driven, thereby bringing the security system into an active state (armed).
When the system is armed while the vehicle is being driven, a vehicle vibration sensor immediately detects vehicle vibrations. As a consequence, the siren suddenly sounds, the vehicle headlights are flashed, the starter is cut off or the supply of the fuel to the vehicle is cut off to thereby stop the vehicle, thus causing great danger.
Therefore, a conventional security system operates so as to avoid receiving all signals such as an arming signal or disarming signal transmitted from the Remocon unit when the ignition switch is turned on to enable the engine.
The conventional security system further has the following described deficiencies.
(1) When the security system is armed by the accidental operation of the Remocon unit when the ignition switch is not turned on, the security system is not in the intended state.
For example, when the security system is armed by the accidental operation of the Remocon unit when the ignition switch is off, the system determines that the movement of the driver or the passenger or the sound from an audio apparatus or the like is abnormal, thereby sounding the siren or flashing the vehicle headlight. Thus, the conventional security system cannot avoid the problem caused by the above-described accidental operation of the Remocon unit. When the passenger or someone unfamiliar with the Remocon unit operates the Remocon unit by accident, the alarm sounds continuously (cannot be stopped) due to the person's unfamiliarity with the Remocon unit, thereby causing serious inconvenience.
The above description is for the case where a Remocon unit located inside the vehicle is operated accidentally. On the other hand, when the Remocon unit is accidentally operated from outside the vehicle, there is the situation where the driver does not want to arm the security system. However, the conventional security system cannot avoid being armed in this situation.
(2) The Remocon unit is often provided with vehicle control keys including a window open/close key in addition to the arming and disarming keys.
However, the conventional security system has the deficiency that the vehicle control functions such as the window open/close control cannot be achieved by use of these keys while the vehicle is being driven.